In a case in which a vehicle is driven in accordance with traffic signals, when a traffic signal ahead of the vehicle is red or yellow, by performing an operation of stopping an accelerator operation and moving the vehicle to coast to a stop position, fuel-efficient driving can be realized.
However, in a case where a vehicle travels at a constant velocity and reaches the vicinity of a traffic signal, when a deceleration operation is performed in accordance with the change in the traffic signal from green to yellow, the fuel-efficiency decreases. On the other hand, if an acceleration operation is performed to forcibly pass the traffic signal, the fuel-efficiency further decreases, and in addition, there is a possibility that an appropriateness of driving operation is imp aired.
Accordingly, from a viewpoint of the fuel-efficiency or safety speed travelling of a vehicle, it is important to know the timing when the traffic signal ahead of the vehicle changes.
For example, Patent Literature 1 discloses the following method: when a server is informed of a distance from a host vehicle to a traffic signal, the server calculates the optimal speed based on the distance to the traffic signal and the time until the traffic signal changes, and the optimal speed is provided to the host vehicle.
Patent Literature 2 discloses the following method: a time when the display of a traffic signal is changed is calculated based on the delay time between when the leading vehicle of a vehicle group stopping behind a traffic signal starts moving and when a target vehicle starts moving, and the distance from the target vehicle to the traffic signal. Then, the information acquired by a plurality of vehicles is integrated in a center to estimate the display change cycle of the target traffic signal.
In each of Patent Literature 3 and Patent Literature 4, a methods of sharing traffic information or the like by forming an ad hoc network based on vehicle-to-vehicle communication for performing data communication between vehicles is disclosed.